Chordate Animals
Objectives:
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Be able to identify the four traits shared by chordates: notochord, dorsal
hollow nerve cord, pharyngeal gill slits/pouches, post-anal tail.
Be able to map the following traits on a phylogeny of the chordates:
Notochord, head (cranium), vertebral column, jaws, lungs, lobed fins,
limbs with digits, amniotic egg, and milk.
Be able to identify to which of the major taxonomic groups an animal belongs
(all taxa indicated in the phylogenetic trees included in this lab).
Be able to describe important features of the animal taxa covered in this lab
Chordate Phylogeny
In the following phylogeny label the following traits: lungs, limbs with digits,
vertebral column, amniotic egg, notochord, jaws, lobed fins, and mammary
glands.
BI 140 Spring 2013 – Chordates lab
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Identifying Chordate Features
The figure below illustrates the 4 traits that chordates have in common:
notochord, dorsal hollow nerve cord, pharyngeal gill slits, and a post-anal tail.
They do not necessarily possess all of these traits at all stages of their life cycle, but
all chordates have these four traits at some point during their life cycle.
 Observe Amphioxus (a Cephalochordate). Draw Amphioxus in the space
below, and label the notochord, dorsal hollow nerve cord, pharyngeal gill
slits, and post-anal tail.
BI 140 Spring 2013 – Chordates lab
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The Tetrapods Move onto Land
When Tetrapods made the move onto land, they faced many of the same
challenges that plants had when they made the big leap onto land.
 What were these challenges?
 What challenges do amphibians face with respect to water availability on
land?
 Why is the amniotic egg considered a key innovation?
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Identifying the major chordate taxonomic groups
Phylum Chordata
Subphylum Urochordata
Tunicates or sea squirts
Tunicates are deuterostomes and chordates, despite looking like a sponge. Even
sponge biologists get confused when looking at pictures or while diving and looking
at a urochordate colony from a distance! But once you cut them open, you can see
tissues and organs. As adults they do not have a notochord, but only briefly during
their larval stage. The specimens we have in our lab today are not very well
preserved, so look at the images your instructor puts on the screen and look at the
diagram in your textbook. Draw a generalized urochordate and at least label the
tunic an the siphons.
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Phylum Chordata
Subphylum Hemichordata
Acorn worms
Acorn worms diverged early from the rest of the chordates, but most interestingly,
the latest data seems to point to them being the sister group to the echinoderms
(starfish and sea cucumbers) that we saw during our last lab. Draw the preserved
specimen, paying
BI 140 Spring 2013 – Chordates lab
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BI 140 Spring 2013 – Chordates lab
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Phylum Chordata
Subphylum Vertebrata
Class Agnatha
The jawless fish
The Agnatha is a paraphyletic group that contains the “jawless fish”. Draw a
specimen from those in the big jar in the lab, and pay special attention to the
structure of the mouth. Compare them against the Gnathostomata (the jawed fish,
which include us the mammals) when you get to those in this lab.
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Phylum Chordata
Subphylum Vertebrata
Class Chondrichthyes
The sharks, skates and rays. This group sits at the base of the Gnathostomata, the
jawed animals. Observe and draw a few specimens. Then look at the phylogeny and
answer this question: are Chondrichthyes lobe-finned fish or are they ray-finned
fish? (hint: it’s a trick question, look at the phylogeny!)
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Phylum Chordata
Subphylum Vertebrata
Class Osteichthyes
The bony fish are part of the ray-finned fish, the Actinopterygii. Observe and draw
some of the specimens on display, taking special note of the fact that they have jaws.
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Phylum Chordata
Subphylum Vertebrata
Class Amphibia
Order Caudata
The salamanders. Amphibians are lobe-finned fish (look at the phylogeny).
Although they are also tetrapods, and thus adapted to the land environment, they
are also tied to the water, and unlike reptiles and mammals, cannot be completely
separated from the water. What is that adaptation that they lack, and which reptiles
and mammals have, that does not allow them to completely move to an
environment without water? Draw at least one salamander, and notice how much
they look like a lizard, although they are not closely related.
Family Caecilidiae
Look and draw the caecilian, another important amphibian. Can you see any legs?
How come it’s still classified as a tetrapod?
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Order Anura
Frogs. Draw a frog, and a tadpole. Are frogs lobe- or ray-finned? Are frogs
tetrapods? Are frogs reptiles? You can answer all of this questions by looking at the
chordate phylogeny.
BI 140 Spring 2013 – Chordates lab
The amniotes
Phylum Chordata
Class Reptilia
Order Crocodilia
Crocs and alligators. Observe and draw the skulls on display.
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Phylum Chordata
Class Reptilia
Order Squamata
Lizards and snakes. This group has scales covering their bodies. Look at the snakes.
How can they be tetrapods when they have no legs? Aren’t tetrapods the animals
with four limbs? Draw a few specimens.
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Phylum Chordata
Class Reptilia
Order Testudines
The turtles. Al turtles have shells. Their placement in the phylogeny of the reptiles is
still debated. Draw a few specimens.
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Dinosaurs
Dinosaurs can be confusing at first because the monophyly of the group depends on
how broad of a definition you use. For example, if you only call dinosaurs those
animals inside the Dinosauria group (within the reptiles, look at the phylogeny of
the amniotes above), and also call birds dinosaurs, then they do form a clade or
monophyletic group. If you exclude birds, then they become paraphyletic. On the
other extreme, if you call a dinosaur any extinct animal for which we find fossilized
big bones, then they are polyphyletic. Look at the phylogeny of the amniotes above.
Using the strict definition of dinosaurs, i.e. only those that are inside the Dinosauria
clade, are the following prehistoric, big-boned animals also dinosaurs: Pterosaurs,
Plesiosaurs, Ichthyosaurs and extinct Crocodilians?
We have on display a large collection of dinosaur models. Using the following
phylogeny, try to find as many as you can. From lecture, remember that there are
two main groups of dinosaurs: the saurischians (the lizard-hipped dinosaurs) and
the ornithischians (the bird-hipped dinosaurs). Look at the phylogeny. Are birds
lizard-hipped or are they bird-hipped?
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BI 140 Spring 2013 – Chordates lab
Notes: